ABSTRACT ? PROJECT 3 Age-related declines in muscle mass and function are major contributors to the loss of mobility and quality of life associated with the physical frailty in the elderly. Our studies showed that mice with skeletal muscle- specific deletion of Sod1 show relatively minor phenotypic changes in muscle mass and function, whereas the loss of muscle mass and function that occurs with whole body deletion of Sod1 could be prevented by rescue of the Sod1 in motor neurons. Data from mice with neuron-specific deletion of Sod1 indicate that this does not fully reproduce the muscle loss that occurs with whole body deletion. Our interpretation of these data is that defective redox homeostasis in motor neurons initiates the processes leading to loss of muscle mass and function which under circumstances of impaired ability of muscle to maintain mitochondrial function, resultant changes in ROS, calcium, and/or inflammation will feed back to further impair maintenance of the NMJ. Previous data from our group showed that whole body deletion of SOD1 leads to dysregulation of redox homeostasis, particularly in mitochondria, and this also occurs in old wild type (WT) mice. The mechanisms by which lack of SOD1 leads to this phenotype are unclear, but changes in neuronal redox appear to lead to a disruption of the structure and function of neuromuscular junctions (NMJ) resulting in loss of muscle redox homeostasis, activation of Nuclear Factor-kappa B (NF-?B) in muscles and increased cytokine generation by muscles. Our working hypothesis is that aging in WT mice, or lack of SOD1 in motor neurons of genetically modified mice, leads to a failure in motor neuron redox homeostasis resulting in disruption of NMJ which when compounded by defective redox homeostasis in the muscle leads to altered muscle mitochondrial ROS and increased generation of pro-inflammatory cytokines. This project will assess this hypothesis through integrated and coordinated Specific Aims: 1. To determine the effects of age or lack of SOD1 on redox homeostasis in motor neurons; 2. To determine whether individual muscle fibers from mice lacking SOD1, old WT mice or neuron-specific Agrin knockout mice show an oxidized redox status that is restricted to those fibers with disrupted NMJ; 3. To determine whether muscle fibers from mice lacking SOD1, old WT mice or neuron-specific Agrin knockout mice show activation of NF?B and increased pro-inflammatory cytokine generation that is restricted to those fibers with disrupted NMJ. We will achieve these Aims through experiments interlinked with those proposed in Projects 1 and 2 and utilize common animal models generated by the Transgenic Animal Core.